Fully-resolved DNS study of rotation behaviors of one and two particles settling near a vertical wall

An Experimental Study of Wall Effect on a Hot Settling Sphere in a Newtonian-Fluid-Contained Block Using Photography

In this study, the effect of temperature on the velocity and trajectory of a hot sphere falling in a water block was experimentally investigated. The sphere, 12 mm in diameter, was thrown through the water inside an enclosure at the ambient temperature by an electromagnetic attachment mechanism, and the particle velocity was recorded by a high-speed camera at 2000 fps. Then, using an image-processing algorithm, the real-time particle location was extracted and its velocity was measured. The results of the cold sphere falling test were compared with those obtained from the numerical solving by the governing equations. An electric heater was used to heat the sphere up to 100, 200, and 300 °C in order to investigate the effect of temperature on the sphere. The sphere was thrown upon reaching the desired temperature. By increasing the temperature, the sphere’s velocity was increased up to around 40% of the velocity of the cold sphere. Further, the sphere was thrown from a point in the vicinity of the wall to investigate the wall impact on the particle movement. This led the sphere to deviate from its trajectory, with the deviation in the cold sphere being negligible, i.e., around 30% of the sphere’s diameter. However, the rate of deviation was much more notable upon increasing the temperature. The deviation start point varied depending on the sphere’s temperature, with the highest deviation that was observed for a sphere with a temperature of 100 °C. Ultimately, the sphere traveled in a more extended way, with no deviation from the main trajectory, when its temperature was increased.

Near-Wall Settling Behavior of a Particle in Stratified Fluids

The phenomenon of near-wall particle settling in a stratified fluid is an emerging topic in the field of multiphase flow, and it is also widely found in nature and engineering applications. In stratified fluids, particle settling characteristics are affected by the physical and chemical properties of the upper and lower fluids, the particle size, the particle density, and the initial sedimentation conditions. In this study, the main objective is to determine the effect of liquid viscosity and particle density on the detaching process, and the trajectory and velocity of near-wall settling particles in stratified fluids. The inertia and velocity of the particle had a greater impact on the tail pinch-off model in low-viscosity lower fluids; that is, the lower the inertia and velocity, the more apparent the order between deep and shallow seal pinch-off. In comparison, in high-viscosity lower fluids, the tail pinch-off models of different inertia and velocity particles were similar. In terms of particle trajectory, the transverse motion of the particle in the low-viscosity lower fluid exhibited abrupt changes; that is, the particles moved away from the wall suddenly, whereas in the high-viscosity lower fluid, the transverse movement was gradual. Due to the existence of the wall, the transverse motion direction of the free settling particles in the stratified fluid, which is determined by the rotation direction of the particles, changed to a direction away from the wall regardless of the particle rotation direction. This transverse movement also caused the particle settling velocity to drop suddenly or its rising rate to decrease, this is because part of the energy was used for transverse motion and to increase the transverse velocity. In our study, the near-wall settling of particles in a stratified fluid mainly affected the particle trajectory; that is, forced movement away from the wall, thus changing the particle velocity. This characteristic provides a new approach to manipulate particles away from the wall.

Immersed boundary method for multiphase transport phenomena

Multiphase flows with momentum, heat, and mass transfer exist widely in a variety of industrial applications. With the rapid development of numerical algorithms and computer capacity, advanced numerical simulation has become a promising tool in investigating multiphase transport problems. Immersed boundary (IB) method has recently emerged as such a popular interface capturing method for efficient simulations of multiphase flows, and significant achievements have been obtained. In this review, we attempt to give an overview of recent progresses on IB method for multiphase transport phenomena. Firstly, the governing equations, the basic ideas, and different boundary conditions for the IB methods are introduced. This is followed by numerical strategies, from which the IB methods are classified into two types, namely the artificial boundary method and the authentic boundary method. Discussions on the implementation of various boundary conditions at the interphase surface with momentum, heat, and mass transfer for different IB methods are then presented, together with a summary. Then, the state-of-the-art applications of IB methods to multiphase flows, including the isothermal flows, the heat transfer flows, and the mass transfer problems are outlined, with particular emphasis on the latter two topics. Finally, the conclusions and future challenges are identified.